Oh, the poor thing! I'm so happy you rescued her. She is sooo skinny. Poor little baby.
The foot and the white mark are very odd. Was she being kept on calci-sand or anything like that? It doesn't look to me like a burn or necrosis... it almost looks as though it has been 'dyed' that colour by maybe a grey or white calci-sand. Can you tell if she has any sensation in the foot?